As for a watching system, Patent Literature 1 listed below proposes receiving data of detection both from a human detection sensor installed in a home of a person as a target to be watched and from an acceleration sensor that the resident wears, to make judgments on activities and conditions of the resident and events occurring in the home. On the other hand, Patent Literature 2 listed below proposes a mastication movement detection device in which the number of mastication movements is counted based on a detected waveform received from a detector that is placed in an external auditory canal and detects an amount of deformation of the external auditory canal. Also, as for cartilage conduction, which has been discovered as a third conduction route in addition to the long-known air conduction and bone conduction, Patent Literature listed below describes that vibration generated by a vibration source contacting an ear cartilage around the entrance part of an external auditory canal causes air-conducted sound to be generated from a cartilage surface inside the external auditory canal, and the generated air-conducted sound then proceeds through the inside of the external auditory canal to reach an tympanic membrane.